This invention relates to an extruder, and more particularly, to an extruder used in an additive manufacturing device employing a screw drive.
Additive manufacturing devices such as 3-D printers build up an object layer-by-layer by extruding a filament material onto a support surface. The quality of the object produced depends in large measure on tight control of the flow rate of filament material through the extruder in conjunction with control of the X-Y position of the extruder head as it traverses an area to build up a layer.
A prior art extruder system is shown schematically in FIG. 1. Filament material 10 passes through a pinch roller feed system 12 that drives the filament material 10 downwardly into a liquefier chamber 14. Thereafter, filament material is discharged through a nozzle 16 onto a scaffolding 18. The pinch roller system 12 engages the filament material 10 on each side as it drives the filament material into the liquefier chamber 14. The driving force that can be achieved with the arrangement in FIG. 1 is limited. Further, the arrangement shown in FIG. 1 is not as accurate as desired because of step size limitations in motor systems driving the pinch rollers.
It is also known to use an internally threaded nut to drive a filament into a liquefier chamber. In this case, the filament passes thorough an internally threaded nut which, upon rotation, drives the filament material linearly. However, the nut rotation puts an unwanted torque on the filament, causing it to distort as it is driven linearly.
An object of the present invention is a screw drive employing counter-rotating elements to substantially eliminate the unwanted torque while driving the filament into the extruder.